Inverter circuits are known which receive a reference signal input of a frequency related to a rotational speed setting signal and generate three pulse-width modulated sine waves each having a 120 degree phase difference. An overcurrent caused by motor overloading, a simultaneous ON condition of series switching elements or the like may be detected as an overcurrent detection signal by an overcurrent detection resistance and an overcurrent detection circuit which controls a protection operation. An appropriate overcurrent detection resistance value is selected depending on the characteristics and capacity of a motor to be controlled, for example, its overcurrent protection level must be set in the range of approximately 10 A-50 A. If the known type of inverter circuit were formed as a hybrid integrated circuit, including the overcurrent detection resistance, it would be necessary to prepare a large number of hybrid integrated circuits to provide the desired range of overcurrent protection levels.